Why Your Performance Charts Are Wrong: Actually, they're probably not, but the results we obtain from them can be way off. A wide variety of factors can be responsible.

Even if your technique is good, even if the runway is truly flat and even if the airplane has a fresh engine, it's unlikely you can obtain the same takeoff roll as the factory pilots, or get down and stopped on the local golf course's fairway. For example, just about any takeoff performance chart for a CAR 3/Part 23 airplane will include a disclaimer to the effect that the results presume a paved, dry, level runway. AIRCR AFT SY STEMS WHICH WAY THE WIND BLOWS A constant element of runway performance calculations is the wind component - its velocity relative to the runway and how it affects the airplane's groundspeed when taking off or landing. [Extracted from the article]